In so-called progressive die systems, workpieces formed from strip stock remain attached to webs that extend along lateral edges of the pieces to facilitate indexing of the workpieces through successive stages of the die assembly. Although such arrangements facilitate conveyance of workpieces through the die stations, they possess the disadvantage that the workpiece must be formed in a linear array at spaced locations along the strip stock, leading to substantial inefficiency and waste. Furthermore, the fact that all workpieces remain interconnected during at least a major portion of the die operation can lead to difficulty and inefficiency in performing operations on the workpieces at a given station. For these reasons and others, so-called die transfer systems have been developed in which the workpieces are pre-separated and fed as individual units of the die arrangement. A die transfer system of this character permits more efficient use of the strip stock material, and also permits greater flexibility in operations that can be performed at the individual die stations. However, the conveyor arrangement for indexing individual workpieces through a die transfer system is more complex than those in typical progressive die systems, usually involving release and reengagement with the workpieces at each of the individual die stations.
U.S. Pat. No. 5,136,874, assigned to the assignee hereof, discloses a die transfer system that includes a lower die, an upper die carried for reciprocal vertical movement toward and away from the lower die to perform at least one operation on a workpiece positioned therebetween, and a conveyor arrangement for sequentially conveying workpieces between the dies. The conveyor arrangement has a pair of conveyors disposed on opposite lateral sides of the lower die. Each conveyor includes a plurality of hands for gripping workpieces, with the hands being spaced from each other lengthwise of the conveyor by distances corresponding to stations of the die. Each conveyor and its associated hands are indexed in a longitudinal direction through the die between stations in synchronism with motion of the upper die. The hands are moved simultaneously in at least one direction perpendicular to the longitudinal indexing direction by a camshaft that extends through the stations along an axis parallel to the indexing direction. A cam is mounted on each camshaft for rotation with the camshaft in synchronism with motion of the upper die. A follower arrangement couples each cam to the hands of the associated conveyor, so that reciprocal rotation of the camshaft about its axis results in reciprocal motion of the hands in one or more directions lateral to the longitudinal direction of conveyance of workpieces through the die stations. The conveyor camshafts are rotated by cam-and-follower arrangements coupled to the upper die, or by electric servo motors controlled by a master controller.
U.S. application Ser. No. 08/549,329, now U.S. Pat. No. 5,680,787, issued Dec. 28, 1997, assigned to the assignee hereof, discloses a die transfer system that includes a camshaft having an axis of rotation parallel to the direction of movement of workpieces through the die system, a transfer bar parallel to the camshaft axis carrying a plurality of hands for engaging the workpieces, and a cam arrangement coupling the camshaft to the transfer bar for moving the transfer bar both horizontally and vertically orthogonal to the camshaft axis. The cam arrangement includes a cam arm coupled to the camshaft and having a pair of angularly spaced drive rollers mounted thereon. Separate horizontal and vertical cam follower slots are disposed adjacent to the cam arm for sequential driving engagement by the rollers on the cam arm, such that rotation of the camshaft and cam arm brings the rollers into sequential engagement with the cam follower slots for driving the transfer bar horizontally and vertically with respect to the lower die.
Although the die transfer systems and indexing conveyor arrangements disclosed in the noted patent and application address and overcome problems and deficiencies theretofore extant in the art, further improvements remain desirable. For example, the indexing conveyors disclosed in the noted patent and application, as well as conveyors of conventional designs, typically are constructed such that the ends of the transfer bars are cantilevered from the supports that couple the transfer bar to the reciprocation drives. The transfer bar ends thus are subject to cyclic vibrations during operation. It is a general object of the present invention to provide facility by means of which such vibrations, particularly vibrations in the vertical direction, are countercyclically damped at one or both ends of the transfer bar.